The overall goal of this project is to study the neurohumoral receptors in normal cardiac growth and during compensatory hypertrophy. Because of their important regulatory role in cardiac physiology, our first priority will be to study the autonomic neurotransmitter receptor binding sites. We will utilize the potent and speciic muscarinic cholinergic antagonist, 3-quinuclidinyl benzilate and the potent Beta-antagonist, (-)-alprenolol, radiolabelled to a high specific activity. The specific binding assays in cardiac homogenates has already been optimized in cardiac homogenates. Thus, we can directly determine the number of receptors in each cardiac region of the normal and failing heart and answer the question, "Is the altered pharmacological response of the hypertrophied heart a consequence of a reduction in the number of receptors/unit mass or does new receptor synthesis parallel increasing ventricular mass? Using the fetal mouse heart in organ culture and sonomicrometer methods, we will examine the time course of appearance of inotropic responses. Using the receptor ligands of high specific activity and high affinity, we will be able to answer the question, "Is the receptor differentiated and intact before an inotropic response in present?" The application of methods and results from the work with autonomic receptors will permit correlative studies in human pathological studies obtained at surgery or post mortem. In addition, other agonists with positive inotropic effects on cardiac tissue will be studied. Purification of the cardiac receptor is also an important goal. In conclusion, the study of neurohumoral receptors in growing and hypertrophied hearts will lead to important insights into the mechanism of clinically important pharmacological agents.